使用 Spring Data JPA 获取固定数量的记录

Question

我正在尝试创建一个 Spring Boot 应用程序，我需要从数据库中获取记录并为从数据库中获取的每条记录调用 REST API。但是，我不想一次获取所有记录，而是想批量检索，比如 10 个，让其余的调用它们，然后再获取 10 个并做同样的事情，直到最后一条记录。我正在使用 spring-data-jpa。我怎样才能做到这一点？

P.S.：它是一个多线程调用，数据库是 Amazon DynamoDB

到目前为止我的代码：

控制器：

//Multi Threaded Call to rest
@GetMapping("/myApp-multithread")
public String getQuoteOnSepThread() throws InterruptedException, ExecutionException {
    System.out.println("#################################################Multi Threaded Post Call######################");
    ExecutorService executor= Executors.newFixedThreadPool(10);
    List<Future<String>> myFutureList= new ArrayList<Future<String>>();
    long startTime=System.currentTimeMillis()/1000;


    ***//Here instead of fetching and calling Mycallable for each one, I want 
    // to do it in batches of 10***

    Iterable<Customer> customerIterable=repo.findAll();
    List<Customer> customers=new ArrayList<Customer>();
    customerIterable.forEach(customers::add);


    for(Customer c:customers) {
        MyCallable myCallable= new MyCallable(restTemplate, c);
        Future<String> future= executor.submit(myCallable);
        myFutureList.add(future);
    }

    for(Future<String> fut:myFutureList) {
        fut.get();
    }
    executor.shutdown();

    long timeElapsed= (System.currentTimeMillis()/1000)-startTime;

    System.out.println("->>>>>>>>>>>>>>>Time Elapsed In Multi Threaded Post Call<<<<<<<<<<<<<<<-"+timeElapsed);
    return "Success";

}

我的可调用对象：

@Scope("prototype")
@Component
public class MyCallable implements Callable<String>{

  private RestTemplate restTemplate;
  private Customer c;

  public MyCallable(RestTemplate rt, Customer cust) {
        this.restTemplate = rt;
        this.c = cust;
    }

@Override
public String call() throws Exception {

    System.out.println("Customer no"+ c.getId() +"On thread Number"+Thread.currentThread().getId());
    restTemplate.postForObject("http://localhost:3000/save", c, String.class);
    return "Done";

}

}

我怎样才能做到这一点？

Answer 1

Spring Data JPA 提供Page 和Slice 来处理这种情况（见PagingAndSortingRepository 和Pageable）

public interface PagingAndSortingRepository<T, ID extends Serializable> 
  extends CrudRepository<T, ID> {

  Iterable<T> findAll(Sort sort);

  Page<T> findAll(Pageable pageable);
}

您可以将可分页请求创建为：

Pageable firstPageWithTwoElements = PageRequest.of(0, 2);

并将其传递给您的自定义存储库（应扩展 PagingAndSortingRepository）：

Page<T> pageResult = customRepository.findAll(firstPageWithTwoElements);